Instrument for measuring electric currents



Sept. 24, 1929. A. N. ANDERSON v INSTRUMENT FOR MEASURING ELECTRICCURRENTS Filed Sept. 2, 1927 Patented Sept. 24, 1929 1,729,320

UNITED STATES PATENT OFFI CE ARTHUR N. ANDERSON, OF GRAFTON,PENNSYLVANIA INSTRUMENT FOR MEASURING ELECTRIC CURRENTS Applicationfiled September 2, 1927. Serial No. 217,283.

This invention relates to the measuring of Figure 1 is a diagrammaticview of one electrical currents, 1n volts, amperes or watts, form ofKelvin balance having my invention and relates more especially todevices of this applled thereto;

kind, commonly referred to as Kelvin bal- Figure 2 is a similar view ofa slightly ances modified arrangement. I In balances of this type asheretofore con- Referring first to the embodiment shown structed therehas usually been provided a in Figure 1, 2 designates a beam which isbalanced beam which is influenced by the curnormally balanced on afulcrum 3. On at rent being measured to close one of two cirleast oneend of the beam 2 there is a windcuits to energize an actuating meansfor a ing 4. Spaced above the winding 4 and second beam. The second beamhas heretostationary with respect thereto is another fore been connectedwith the first beam by winding or coil 5, and below the winding 4 means.of a spring. Whenthe pull of the and stationary with respect thereto isa simispring equals the magnetic pull of the curlar coil 6. The coils i,5 and 6 constitute a rent being measured to restore the balance magnetswhich attract or repel each other.

of the first beam the correct current value is The several windings areconnected in series, ascertained by a pointer actuated through the thecoils 4 and 5 being connected by a flexible movement of the second beam.conductor 5' and the windings 4 and 6 being The use of a spring in adevice of this kind connected by a similar flexible conductor 6. is veryunsatisfactory for the reason that the One side of the coil 5 isconnected by a wire 7, characteristics of the spring are not constant,which is adapted to be included in a circuit and the spring is affectedby temperature and to be tested. One side of the coil 6 isconatmospheric conditions. This necessitates nected with a wire 8, whichis adapted to be frequent adjustment of the spring and testing includedin the other side of the circuit to a of the instrument, as anyinaccuracy of the be tested. When a current flows through the springwill throw the instrument out of wires 7 and 8, the floating magnet 4 onthe proper calibration, beam 2 is attracted by the coil 6 and repelledThe present invention has for its principal by the coil 5. object toprovide an instrument of this type On the end of the beam 2 is a contactmemwherein springs are entirely eliminated and her 9 adapted to makecontact with one or so to provide a flexible weight for counterthe otherof fixed contacts 10 and 11. When balancing the balanced lever, and toprovide the beam is moved down by the action of the means for variablyactuating the weight to several magnets, against the action of therestore the proper balance for the beam to counterbalance hereinaftermentioned, the accurately indicate the value of the current contact 9closes a circuit with fixed contact 10, being measured. and when thecounterweight exerts an over- The invention has for a further object tobalancing effect, the contact 9 closes a circuit provide a weight whichis extremely flexible with contact 11. The contact 10 is in circuit andwhich is not affected by atmospheric or with a wire 12 leading to asolenoid 13 whose temperature conditions, so that its eflect, once th rside is conne ted thr ugh a att ry 14 the instrument has beencalibrated, will be and Wire 15 with the beam, as indicated at 16,nnvarying and repeated adjustment at short t0 make t etu cllcuit ContactT intervals will not be required. contact 11 is in circuit with solenoid13', bat- The nature of the invention may be readily tery 14 and WlI'e15. understood by reference to the accompany- At 17 is a lever supportedon a fulcrum ing drawings which illustrate diagrammatic at 18. Connectedto the lever 17 on one side embodiments of the invention and to the deofthe fulcrum 18 is an armature 19 for the tails of which the invention isobviously not solenoid 13 and connected to the lever 17 at restricted.the other side of the fulcrum is an armature In the drawings: 19 for thesolenoid 13'. 1

Connected to the lever 17 through a system of levers is a pointer 20adapted to move back and forth over the scale 21 according to themovement of the lever 17.

Connected to the end of the balanced beam- 2, opposite the contact 9, isa flexible string or cord, which is preferably of such a nature that itwill not absorb moisture to any considerable extent and which is notmaterially affect-ed by weather conditions 01' by variations inatmospheric temperature. This string, designated 22 has its other endwound about a drum 23, and secured to the string at intervals along itslength are a plurality of small weights 24. The beads or weights 24 maybe of any suitable material, but are preferably of a non-magneticmaterial and are preferably made of glass inasmuch as this material willnot absorb moisture or be affected by atmospheric conditions. The drum23 is rotatable on a fixed support not shown, and is rotated through asegmental rack on an arm 25 whose outer end is pivotally connected at 26with a link 27 pivotally connected to the end of the lever 17 at 28.

In the operation of the device, wires 7 and 8 are connected to a circuitto be, tested, whereupon the magnet 4 will be attracted to the magnet 6,thereby closing the circuit between contacts 9 and 10, to energizesolenoid 13. The energization of the solenoid 13 will attract thearmature 19 down, pulling down on the lever 17 to move the link 27 up,rocking the arm 25 up, thereby rotating the drum 23 to increase thelength of the flexible weight 22. As the weight 22 is lengthened, thecounterbalancing efi'ect thereof is increased, tending to equalize themagnetic force that rocks the beam. When a condition of balance betweenthe counterweight 22 and the lever 2 exists, the current value will beindicated by the pointer 20, which will have been moved by the movementof lever 17 over the scale 21.

If the counterbalance is overbalancing the magnetic attraction, the coilcarrying end of the lever 2 will rise, to close a circuit to solenoid13, thereby moving lever 17 in the other direction, to decrease theeffective length of the counterweight.

It will be seen that the arrangement shown in Figure 1 is merelydiagrammatic, and that such mechanical features may be incorporatedtherein as will insure the proper ratio of movement of the drum 23 forany given movement of the arm 17.

The arrangement shown in Figure 2 is a more practical embodiment of theinvention. In this figure, 3O designates the balanced beam,corresponding to the beam 2 of Figure 1, 31 is the fulcrum, 32 is thecoil at one end of the beam, 33 is the fixed coil above the magnet 32and 34 is the fixed magnet below the magnet 32. At the end of the beam30 is the contact 35 for engagement with the upper contact member 36 orthe lower contact member 36 according to the movement of the beam. Thecoils 32, 33 and 34 are connected in series across wires 38 and 39 towhich the circuit to be tested is connected. Contact 36 is in circuitwith a wire 37 leading to a reversible motor 40,. The other side of themotor 40 is connected through a battery or other source of current 41 tothe beam 30 at point 42 and through the beam is connected to the contact35. The cont-act 36 connects through another wire 43 with the reversiblemotor 40. The circuit through contact 36 is arranged to drive the motor40 in one direction while the circuit through contact 36 drives themotor 40 in the opposite direction. The motor 40 drives the drum 44corresponding to drum 23 of Figure 1. Wound about this drum is one endof the flexible weight 45, which is comprised of a cord with weightsdistributed therealong, as described in connection with Figure 1, andthe other end of this flexible weight is connected to one end of thebeam 30.

The drum 44 is geared through a sprocket or in any other suitable mannerwith a pointer 46 movable along the scale 47.

In the operation of the arrangement herein shown the circuit to themotor 40 will be closed when the coil 32 is attracted-toward the coil34, and the motor 40 will be driven in a direction to unwind theflexible weight 45 until a balance has been reached. As the drum isrotated by the motor to unwind the weight to increase its eflectivelength, the indicator 46 is correspondingly moved with respect to thescale 47 and the value of the current to be measured is thus indicated.If the counterweight is too heavy, the contact 35 is moved into contactwith the contact element 36 and the motor 40 is driven in the oppositedirection to decrease the effective length of the counterweight 45.

While the general type of instrument herein described is admittedly old,my invention consists in the provision of a variable counterweight whoseeffective length is increased or decreased according to the movement ofthe balanced beam, whereby springs heretofore provided in devices ofthis nature can be I eliminated. The weight amployed is of an extremelyflexible nature, so that very fine increments of measurement areobtainable and the device is immune to changes of temperature andatmospheric conditions in so far I as the variable counterweightisconcerned. A further advantage of the invention resides in theprovision of means for automatically varying the efi'ective length ofthe counterweight to counterbalance the magnetic ati traction to restorethe balanced beam to a neutral position, and thereby accurately indicatethe value of the current to be measured.

While I have illustrated two embodiments of my invention, it Will beunderstood that i the invention is not confined to the articulararrangement of parts therein disc osed, and that it may be otherwiseembodied within the spirit of my invention and under the scope of theappended claims.

I claim:

1. In an a paratus of the class described, a lever, an e ectromagneticmeans for moving the lever out of normal position, a flexiblecounterweight attached to the lever including a flexible element havingweights distributed therealong, andmeans for varying the effectivelength of said variable counterweight, said means including anelectrically responsive element controlled by the movement of saidleverl 2. ln an apparatus of the class described, a lever,electromagnetic means for moving the lever out of a normal position, aflexible counterbalance for returning the lever to normal position andelectrically operated means controlled by the movement of said lever foreifectively lengthening or shortening the counterbalance.

3. In an apparatus of the class described, a balanced lever,electromagnetic means for moving the lever in one direction outof anormal balanced position, a variable counterweight associated with thelever for counteracting the influence of said electromagnetlc means, andmeans controlled by the lever for operating the variable counterbalance.

i. In an apparatus of the class described, a balanced lever,electromagnetic means for moving the lever in either direction out ofneutral position, a flexible counterweight attached to the lever, a drumover which the counterweight is wound, and means responsive to themovement of the lever for rotating the drum to vary the effective lengthof the flexible counterbalance whereby the influence of saidelectromagnetic means may be counteracted, and an indicator movablesynchronously with the drum.

5. In an apparatus. of the class described, a pivoted lever,electromagnetic means for moving the lever out of normal position, acounterweight for restoring the lever to normal position against theinfluence of said electromagnetic means, a contact element on the end ofthe lever, a fixed contact with which the first mentioned contact makescircuit when the lever is out of normal position, and electric means incircuit with said contacts for o crating the variable counterbalance,where y the lever may be automatically returned to normal positionagainst the influence of said electromagnetic means.

6. In an apparatus of the class described, a pivoted lever,electromagnetic means for moving the lever out of normal position, acounterweight for restoring the lever to normal position against themfluence of said electromagnetic means, a contact element on the end ofthe lever, a fixed contact with which the first mentioned contact makescircuit when the lever is out of normal position, and electric means incircuit with said contacts for operating the variable counterbalance,where y the lever may be automatically returned to normal positionagainst the influence of said electromagnetic means, and an indicator 0eratively connected with said counterweig t operating means.

7. In an apparatus of the class described, a balanced lever,electromagnetic means for rocking the lever, and a counterweightattached to the lever including a flexible cord havinlg weightsdistributed therealong.

8. 11 an apparatus of the class described, a balanced beam,electromagnetic means for rocking the beam, a contact movable with thebeam, fixed contact members with which the first mentioned contactmember'may engage when the lever is rocked to either limit of itsmovement, a flexible counterweight associated with the lever forcounteracting the attraction of said electromagnetic means, electricmeans for operating the flexible counterweight, one of said fixedcontacts being in a circuit with said electric operating means in suchmanner as to cause said operating means to increase the efiective lengthof said flexible counterweight when contact is made therewith, the otherfixed contact being in circuit with said elec-' tric operating means tocause the effective v. length of the flexible counterweight to bedecreased when the circuit thereto is closed.

9. In an apparatus of the class described, a balance beam movable inopposite directions from a normal position between certain limits,electromagnetic means for moving the beam in one direction out of itsnormal balanced position, circuit closing means associated with thelever for closing independent circuits when the lever is at either limitof its movement, a variable counterweight connected with the lever, areversible actuating means for the counterweight, said contact closingmeans being in circuit with said reversible actuating means foreffecting oper ation thereof in reverse directions respectively.

10. A measuring means for electric currents including a balanced beam,electromagnetic means for actuating the beam out of its normal balancedposition, contacts closed by the predetermined movement of the beam ineither direction from its normal position, a flexible counterweightconnected with the beam, reversible means for .varying the eflectivelength of said flexible counterweight, one of said contacts beingarranged for effecting the movement of said reversible actuating meansin one direction when the circuit thereto is closed and the other ofsaid contacts being arranged to effect the operation of the reversibleactuating means in the opposite direction when contact is madetherewith, and

an \indicator operated through the movement of said reversible actuatinmeans.

11. The combination wit a measuring device of the Kelvin balance typehaving a balance beam therein, of a variable counterweight of a flexiblenature attached thereto, and means for varying the effective length ofsaid counterweight.

12. The combination with an electric current measuring device of theKelvin balance type wherein a balance lever is employed, of a flexibleelement having one end connected to the beam, the other end of saidelement being connected to a reversible operating means, circuits forreversely operating the said operating means upon a predeterminedmovement of said beam in reverse directions from a neutral position, andan indicator actuated by said reversible operating means.

In testimony whereof I have hereunto set my hand. x -1.

ARTHUR N. ANDERSON.

